The sensitivity to light variation per retina point is tested during an examination of the field of vision. Two different methods are known, namely, one is known as a kinetic perimetry method, in which the examination is carried out with a moving testing mark, while in the case of the static perimetry method, the sensitivity to the difference in light coming from dark luminous densities is measured exactly at a fixed point. Computer-supported systems are mostly utilized today. These systems operate according to the so-called raster or screening perimetry method. According to one program, a testing-point raster is automatically screened, either with adjusted testing-point brightness or with an exact threshold measurement, the results being then stored and printed out at the end of an examination. Areas, where no recognition or a reduced sensitivity to light variation exists, are marked separately. The earlier the deficiencies are recognized, the more favorable is the prospect for a successful treatment.
Spherical perimeters are mostly used in examinations of the field of vision, in which either the testing point is projected into the sphere through an adjustable projection system or even diode photoconductors or glass fiber photoconductors are mounted in the sphere. These known systems are all rather complicated and mechanically very sensitive, since the highest demands are made on precision.
U.S. Pat. No. 4 634 243 discloses a method for the examination of the field of vision, in which a flicker pattern image is shown to the person tested. The image contains a regular arrangement of image points in the form of a geometrically constant, limited pattern. This pattern, which is small in comparison to the entire surface of the image, has regularly arranged points of the same density, which differ both from the arrangement and also from the density of the points of the flicker field. To determine visual field defects or similar vision defects, this geometrically arranged dot pattern is moved over the entire image. Thus a scanning of the center field of vision of the volunteer patient up to 30.degree. occurs. Also this method has proven to be disadvantageous, since scanning of the entire field of vision by means of complicated and long lasting examinations is necessary.
A problem in all of these examinations of the field of vision is that the person tested is not able to determine whether or not losses in the field of vision exist. Thus the entire retina must be examined during each examination. The examination could be carried out in a much simpler fashion and in much less time if it were known already at the start of the examination where such field of vision losses are to be expected
The purpose of the invention is to provide an apparatus and a method for finding scotomas in the eye of a person tested enabling himself or herself to indicate such field of vision losses within a very short period of time.
According to the invention, to the eye of the person tested is thus offered an image on a screen, which consists of a plurality of dots which lie closely side-by-side, the brightness of which dots changes continuously, with the image additionally having a fixation point for the eye. The change in the brightness of the individual image dots can occur regularly or periodically. The simplest apparatus for carrying out the perimetric examinations has proven to be a high-resolution video monitor having a randomly flickering display with a very small grain, similar to a flicker field which results when an interference or breakdown occurs in televisions. The eye of the volunteer patient is spaced a predetermined distance from the video screen with the eye being fixed on a specific fixation point on the image screen. Viewing the flicker field, the person tested can determine within seconds at which areas scotomas exist.
The described abnormal scotomas can be made clearly visible if the patient looks, instead of onto a homogeneous surface, onto a light-dark small grain surface which flickers at a high frequency, similar to the surface of the flicker field on a switched-on television monitor when no program is being received. When the view of the patient is fixed by a clearly visible point fixedly located in the center of the television screen or programmed to be faded in, the visual field defect is sensed as an area which flickers less or not at all, the brightness of which area clearly differing from the surrounding area. The observer can trace the scotoma boundaries with the finder exactly on the television screen. This marking of the patient's own scotomas occurs mostly spontaneously without a special request, because the impression of the limited "cloud" in the flicker field is very impressive for the patient. All recorded absolute scotomas, which have been created through damage to the retina, the optic nerves, the chiasmas or the tractus opticus, can be indicated by the patient in the same manner as done for scotomas or vision losses caused by glaucoma--although it can presently not as yet be recognized when a scotoma is noticed as a lighter and when as a darker cloud. However, in every case the scotoma is noticed by the flickering of the flicker field being in its area sensed not at all or less than in the surrounding area.
A condition facilitating a reproducible noticing of the scotomas by the patient and a quick perimetric control and registration of the noticed field of vision loss is a video monitor on which both a standardized flicker field, produced by a computer and changeable only in its parameters, and also a contourless surface, with freely movable, selectively light or dark testing points, can appear. Furthermore it is advantageous to fade in a field of vision pattern having degree information onto the video monitor to facilitate recognition of the position and expanse of the vision losses.
The noticing of the scotoma in the flicker field can be associated in a very simple manner with a perimetric measuring examination on the screen of the same monitor as a test field. Noticing of the scotoma in the flicker field thus plays the role of a first orienting test, i.e. a screening method whereby within seconds the ophthalmologist is informed whether and where vision losses in the 30 degrees field of vision exist. Subsequently, it is possible to associate in the scotoma area a manual kinetic perimetry of the common type or an automatic raster perimetry. The advantage of such a two-sided method lies in the perimetry measuring having to be carried out only in areas of vision loss which, compared with the present methods, means a considerable savings in time.
The simultaneous use of a high-resolution video monitor both for the flicker field perimetry and also the conventional perimetry permits an exact comparability of the obtained examination results. Contrast, brightness and color can be changed in the same manner in both types of examination. The kinetic and also the static perimetry methods can be carried out either freely movably by hand or, however, also automatically. The type of campimetric procedure can thereby be adjusted completely to the shape and size of the field of vision losses discovered previously with the flicker field perimetry. In this manner, it is possible to relate the advantages of the very quick discovery of scotomas with the exactness of a campimetric method adjusted to the situation.
In dependency on the size of the video monitor results the tested field of vision area. The field of vision area lies at 60 degrees in normal video monitors. The field of vision area can, however, be enlarged by moving the fixation point.
It has been found to be particularly advantageous when the flicker image is projected in a perimeter hemisphere, because it is then possible to carry out the advantages of the double-track perimetric method also in the form of a hemisphere perimetry.
It is particularly advantageous in the inventive apparatus if a brightness adjustment of the image or of the image screen can be carried out at a specific testing or measuring point. This adjustment can occur for example with the help of a photodiode with the current flowing through the photodiode serving as a measurement of the brightness of the image screen. The adjustment can be carried out both continuously during the examination and also at regular intervals. Thus it is possible to adjust and examine precise luminous density graduations in order to achieve reproducible examination results. According to the invention, it is also possible to carry out the luminance threshold at several image points.
It is also possible by means of the inventive apparatus to occupy only those areas of the field of vision with a flicker pattern which have already been identified as areas of vision defects by the person tested. If the remaining image does not show any flickering and the person tested states that the entire image is without a flicker pattern, then the field of vision loss has been proven positively. In order to permit the flicker image to appear only on the predetermined surface portion, the apparatus is provided with a light pen, a mouse or a touch screen.
It is inventively provided to shift or move the image to adjust the fixation point in order to adjust the fixation point to the position of the eye of the person tested. This shifting can be done by means of a computer program with a coordinate system being for example offered to the eye of the person tested. This possibility of adjustment offers the advantage that the conventional complicated apparatus for the fixation and adjustment of the tested person's head can be abandoned. Furthermore, the adjustment of the fixation point can be carried out substantially quicker and simpler.
It is possible according to the invention to change the diameter of the image points in order to permit persons having ametropic eyes to recognize the individual image points. Furthermore, it is possible according to the invention to provide different colors for the image points or color changes to prevent the person tested from adapting the eye to the flicker image. It is furthermore possible to vary the frequency of the change in brightness of the image points in order to make an acclimatization of the patient impossible. With a color change of the image points it is at the same time possible to test the color vision of the person tested.
It is possible by means of the inventive apparatus to verify the position of the scotomas through a positive-negative reversal of the brightness of the individual images.
To make the fixation of the eye of the patient easier, it is possible by means of the inventive apparatus to fade, for example, number series into the computer-controlled image, with the determination of the fixation point being able to occur by the person tested stating which number or which numbers of these series he sees. The fixation of the eye can be controlled by bringing the blind spot of the person tested, at which he sees nothing, into conformity with the fixation point or fixation area. The size of this fixation point or fixation area, that is of an image loss produced by the computer, is smaller than the blind spot itself. The person tested will thus already during a small change of the fixation of the eye be able to immediately determine a change.
A further advantage of the inventive apparatus lies in a plurality of finely graduated gray values being able to be illustrated in on the image, for example, when using a common television screen having 256 gray values. It is thus particularly easy to carry out threshold measurements.
A particularly favorable further development of the inventive apparatus exists in giving the treating person, for example the physician, a second screen, so that he will at any time be informed regarding the position and size of the respective fields of loss.
It has proven to be particularly advantageous with respect to the inventive method to effect, for the purpose of an early recognition of glaucoma, an artificial increase of the pressure on the eye of the person tested. This may be done for example through a suction pump or through medication. It is possible in this manner to predetermine the vision defects which would occur during a natural change of the pressure on the eye.
The capability of easily noticing one's own field of vision losses in the flicker field has still further advantages. It enables interested patients to themselves control their scotomas at home at the television screen. They only must be informed that they must keep at all times the same distance from the screen (approximately 30 cm.), that they must cover one eye and that furthermore a still fixation with the help of a fixation point must be assured. A possible enlargement of the blind spot or the occurrence of new scotoma areas can then be discovered by well observing patients at home using their own television set.